Binder of dhsocyanate modified unsaturated polyester and vinyl chloride polymer and method of preparing same



United States Patent BINDER OF DIISOCYANATE MODIFIED UNSATU- RATED POLYESTER AND VINYL CHLORIDE :OLYMER AND METHOD OF PREPARING John A. Parker, Lancaster Township, Lancaster County, Pa., assignor to Armstrong Cork Company, Lancaster, Pa., a corporation of Pennsylvania No Drawing. Application September 26, 1955 Serial No. 536,736

14 Claims. (Cl. 260-454) This invention relates generally to surface covering materials, and to binder systems for such surface covering materials. More particularly, it relates to surface covering materials and binder systems therefor wherein the binder system comprises an intimate blend of polymerized vinyl halide and diisocyanate-modified polyester.

In recent years, a tough, resilient, plastic surface covering material has been produced by forming a composition containing filler and binder wherein the binder includes a polyvinyl resin and a butadiene-acrylonitrile copolymer. The composition is then calendered into a sheet and cured in air at elevated temperatures to form the surface covering material. The basis of the binder of the composition is a mixture of polyvinyl chloride and a butadiene-acrylonitrile copolymer, which copolymer advantageously contains 40%70% by weight of butadiene and about 30%60% by weight acrylonitrile. Such a mixture may be obtained by the method described in Henderson Patent No. 2,330,353, in which a polyvinyl chloride and bntadiene-acrylonitrile copolymer are compounded by milling the polyvinyl chloride into the copolymer until a homogeneous mass is obtained. Although surface covering materials fabricated from a binder system as described above have beensatisfactory, there is always the need for other binder systems which possess desirable properties to an even greater extent than can be obtained from those currently available. Although a great deal of research work has been done with a view toward utilizing polyesters as a component in such a binder system, no outstanding results have yet been achieved. This has been true because the specifications for a binder system for surface covering materials are stringent indeed. It is impossible to predict the behavior of a component of a binder system save for the fact that the physical properties of most components obviously exclude their possible use in such binder systems. Requirements of flexibility, strength, wet and dry abrasion resistance, alkali resistance, and processibility on the equipment used to form surface covering materials have so far prohibited the use of polyesters, particularly diisocyanate-modified polyesters, in binder systems for surface covering materials. Although it has been recognized that such polyesters might hold promise in the surface covering materials field, none has yet been forthcoming.

Thus, it is the primary object of the present invention to present surface covering materials having a binder system which utilizes a diisocyanate-modified polyester.

It is a further object to present a novel binder system for such material. It is still a further object of the present invention to present a method for making surface covering materials and a binder system therefor, which materials may be prepared and processed on equipment normally in use in the surface covering industry.

To this end, the invention contemplates a binder system for surface covering materials comprising an intimate blend of polymerized vinyl halide and diisocyanatemodified polyester. The modified polyester is the reaction product of just sufiicient organic diisocyanate with unmodified polyester to form a gel. The unmodified polyester must have an acid number in the range of about 2-15, preferably about 4-6, and a hydroxyl number in the range of about 20-55, preferably about 30-40, and is formed from a saturated glycol having 4-6 carbon atoms, a saturated dibasic acid having 6-10 carbon atoms, and a dibasic acid possessing a single unsaturated bond and having no more than 8 carbon atoms. The saturated acid and the unsaturated acid are present in the polyester in a mole ratio of about 2:1. The surface covering material of the present invention is prepared by blending the above-described binder and a filler, the filler being present in an amount in the range of about l5%-75% by weight. The filled composition may be cured at elevated temperatures in air or in presses and may be in the form of sheets or tiles and may be backed or unbacked.

The polyester utilized in the present invention is one having narrow and critical properties; this is true in view of the extremely restricted properties demanded in surface covering applications, as mentioned above. The polyester may be prepared in unmodified form only from three classes of ingredients. The first ingredient must be a 4-carbon saturated glycol, as for example 1,3- butylene glycol, 1,4-butylene glycol, diethylene glycol, and the like. The second ingredient must be a saturated dibasic acid having a carbon chain of 6-10 carbon atoms, as for example adipic, sebacic, azaleic, methyl adipic acid, and the like. The third ingredient is a dibasic acid possessing a single unsaturated bond and having no more than 8 carbon atoms, as for example tetrahydrophthalic, maleic, fumaric, and similar acids. The ratio of saturated dibasic acid to the unsaturated dibasic acid must be about 2:1 on a mole basis. Generally, the total hydroxyl equivalent in the glycol will equal the total carboxylic acid equivalents in the two acids, except for the fact that it is customary and sometimes essential to use an excess of glycol in the making of polyesters.

The properties of the present polyester are so sensitive to the ingredients used that differences appear even when the ingredients falling within the scope of the present invention are varied. For example, where 1,4- butanediol and adipic acid are used, the resulting properties are excellent. On the other hand, where 1,3- butanediol and adipic acid are used, the properties in the final modified polyester, while good, leave something to be desired. Yet where 1,3-butanediol and sebacic acid are used, the properties in the final polyester again are unusually excellent. Where 1,4-butanediol is used with either sebacic or azaleic acid, the final properties are good, yet not as good as the two formulations described as having excellent properties. In each case, of course, the ratio of the saturated acid to the ethylenically unsaturated acid remains about 2:1. Thus, it can be seen that the properties of the final polyisocyanate-modified polyester are in the present case peculiarly dependent on the precise formulation used.

The preparation of the polyester may be carried out along the lines of known polyester technics. Preferably, the excess glycol may be caused to react with the unsaturated acid at a temperature of about C. Because the unsaturated acid may sublime very readily at higher temperatures, the mixture of glycol and unsaturated acid may be heated until the half ester of the unsaturated acid is formed. The end of the formation of the half ester can readily be seen by the disappearance of the white solid unsaturated acid from the solution, causing the solution to become homogeneous. Maleic anhydride reacts the fastest and usually requires about 5-10 minutes for the formation of the half ester.

Tetrahydrophthalic anhydride and endomethylene tetrahydrophthalic anhydride react more slowly because they are less soluble in the glycol.

Once the half ester is formed, the unsaturated acid is more stable at elevated temperatures. Subsequent to the formation of the half ester of the unsaturated acid, the saturated dibasic acid may be added and the temperature of the mixture may be increased to about 145 C.

During the addition of the unsaturated and saturated acid, an inert gas flow should be maintained through the solution to minimize side reactions that might occur in the presence of air. Most of the unsaturated acids used are sensitive to oxygen and the double bond oxidizes readily. This oxidation of the double bond might lead to cross linking of chains and subsequent formation of a gel, an undesirable reaction at this point. The ease with which the oxidation occurs is dependent upon the unsaturated acid used. The ester containing maleic anhydride and endomethylene tetrahydrophthalic anhydride oxidizes more easily than one containing tetrahydrophthalic anhydride.

After holding the temperature at 145 C. for a suitable period of time, for example about one hour, the temperature may be increased slowly, for example to about 200 C. The time required for this increase of temperature is dependent upon the boiling point of the glycol used. If the boiling point of the glycol is below about 210 C., the time required would be on the order of 2-3 hours, while boiling points above about 210 C. allow a reduction of time to about 1 to about 1 /2 hours.

The temperature should be held at about 200 C. until an acid number of about is obtained. If the glycol boils above about 210 C., the temperature may then be increased from 200 C. to about 220 C.; but for those boiling below about 210 C., the temperature should be maintained at about 200 C. In any case, these temperatures should be maintained at their respective levels until the final end point is reached. In the latter stages of polymerization, Where the acid number is below about 30 and the hydroxyl number is to be lowered further, the rate of decrease of the hydroxyl number may be dependent upon the rate of flow of carbon dioxide or other inert gas and upon the temperature of the polymer. In order to obtain a rapid decrease of the hydroxyl number in the later stages of polymerization, the temperature of the polyester should be above the boiling point of the glycol used and the gas flow increased to such a rate that the volatile glycol is swept from the reaction mixture. For the polyesters to be suitable for use in the present invention, it is necessary to obtain an acid number in the final product in the range of about 215 and a hydroxyl number in the range of about 20-55. A preferred embodiment calls for an acid number in the range of about 5:2 and a hydroxyl number of :5. With these latter limits on acid numbers and hydroxyl numbers, the molecular weight will vary from about 3400 to about 2380.

The chain length of the molecules of the above-described polyesters should then be extended by means of organic diisocyanates. The diisocyanates are organic compounds whose sole reactive groups are at least 2 isocyanate groups. Although the particular diisocyanate to be used is not critical, such considerations as handling hazards, cost, and ease of dispersion make 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, or mixtures thereof, the diisocyanates of choice. Additional diisocyanates which may be used are 4,4'-diphenyl diisocyanate, 4,4- diphenylene methane diisocyanate, 4,4'-tolidene diisocyanate, the naphthalene diisocyantes, and p-phenylene diisocyanate. The proper amount of the diisocyanate should be intimately blended with the polyester, preferably at room temperature, and the mixture then heated to a temperature in the range of about 100150 C. to accomplish incipient gelation.

The precise amount of diisocyanate to be added to a given amount of polyester will vary slightly according to the particular polyester involved, even where identical ingredients are used under purportedly identical conditions. One of the great deterrents to the wide use of diiso cyanate-modified polyesters has been the inability to obtain reproducible results Where polyesters have been made from identical ingredients under apparently identical conditions and have then been reacted with identical amounts of identical diisocyanates. For this reason, it is essential that each batch of polyester be tested to determine the exact amount of diisocyanate needed for that particular batch of polyester if the polyester is to serve as a useful component in the binder system of the present invention. The addition of too little diisocyanate will yield a binder system and a surface covering material fabricated therefrom which is too soft, flexible, and which possesses too low abrasion resistance to serve as a useful surface covering material. On the other hand, an excess of diisocyanate yields a polyester with dangling free isocyanate groups. Such a polyester is Water-reactive, and may be sufficiently cross linked to yield a tough, stiff, and unprocessible binder system completely unsuitable for surface covering materials.

The precise amount of diisocyanate to be added to the polyesters described herein should be that amount needed to give an incipient gel, and no more. It is a fortuitous happenstance that the point of incipient gelation with the particular polyesters described herein yields a polyester of maximum chain length and minimum cross linking, which polyester is preeminently suitable for the binder systems and surface covering materials of the present invention. For any given polyester, this precise amount of diisocyanate may readily be determined by one or the other of two methods.

The first method amounts to an empirical determination. A number of samples of the polyester are Withdrawn at the end of the polyester-forming process. To each of the samples after weighing is added a weighed amount of diisocyanate, the amount being different for each sample. The samples are then heated, for example to a temperature in the range of about 150 C., to accomplish incipient gelation and are then cooled. The sample containing the proper amount of diisocyanate will be that sample which neither flows easily nor sets to a stiff gel. The amount of diisocyanate which will yield a chain-extended polyester wherein an air bubble will either just rise or just not rise will yield the chain-extended polymer which can be used as a component in the binder system for surface covering materials. This amounts to no more than saying that the proper amount of diisocyanate is that amount which yields an incipient gel on one or more samples pulled for that purpose. The point of incipent gelation defines the point where chain extension of the polyester is at a maximum and cross linking has just begun to occur. Generally speaking, the proper amount of diisocyanate will be that amount by weight equal to 0.6-0.9 isocyanate equivalent for each. polyester equivalent; general amounts more accurately stated than this simply cannot be given in the present state of konwledge concerning diisocyanatemodified polyesters.

The second method of determining the precise amount of diisocyanate to be added to a given polyester involves more elaborate analytical technics. "this method is particularly useful where the procedures for making a particular polyester have not been completely developed, and the characteristics of the resulting polyester are not completely understood. The method involves the separation of a sample of the bulk polyester into one or more polyester species by chromatographic methods or by a water-wash method. The individual polyester species are then characterized as to Weight fraction, hydroxyl number, acid number, and the like. The end groups of the polyester chain and their equivalent weights are thus and dibutyl ammonium oleate.

determined. Using weighted averages according to the characteristics of the various polyester species,'it is then possible to determine the precise amount of diisocyanate to be added to a given weight of the bulk polyester to yield an incipient gel at which chain extension is at an optimum and cross linking has just begun to occur. This second method is set forth more fully in copending application Serial No. 536,737, filed September 26, 1955.

Once the proper amount of diisocyanate has been thoroughly and intimately dispersed throughout the polyester, the mixture is heated to an elevated temperature to achieve gelation as described above. Subsequently, the diisocyanate-modified polyester may be cooled and utilized with a polymerized vinyl halide to form the binder system of the present invention.

The polymerized vinyl resins to be used in the'binder' system of the present invention may be those low to mevarious vulcanization accelerators, as for'example zinc phenyl ethyl dithiocarbamate, diethyl dithiocarbamate, zinc isopropyl dithiocarbamate, zinc diethyl dithiocarbamate, zinc phenyl ethyl diethiocarbamate, diphenyl guanadine, tetraethyl thiuram disulfide, and tetramethyl thiuram disulfide. Plasticizers such as tricresyl phosphate, dibutyl phthalate, m-alkyl toluene sulfonamide, and other known plasticizers may be added. Stabilizers or antioxidants such as hydroquinone, n-phenyl alpha naphthalamine, nphenyl beta naphthalamine, N,N-exomethylene-bis-orthohydroxybenzamide, sodium acid phosphate, dibutyl tin laurate, and others known in the art may be used. The total amount of the compounding agents exclusive of the fibrous and nonfibrous filler generally runs up to about 10% by weight of the filler.

In an advantageous embodiment of known processes,

' the filler-binder mixture to be calendered is characterized dium molecular weight polymerized vinyl halides available in commerce. Exemplary of such resins are those polyvinyl resins made by the Bakelite Company and bearing the designations VYMF, VYVF (copolmer of vinyl chloride containing about 13%-5% vinylacetate), VYNW, VYI-IH (vinyl chloride copolymer containing about 13% vinyl acetate), and mixtures thereof. Additionally, the Geon resins sold by B. F. Goodrich Chemical Company, in particular those designated as Geon 121 and Geon 126, are suitable. The most significant property of the polymerized vinyl halide resin suitable for use in the binder system of the present invention is that of yielding a hard, tough, and otherwise suitable surface covering material after being plasticized with the sulfur-curable diisocyanate-modified polyesters described above, and thereafter admixed with suitable fillers and other ingredients to be described later and formed into a surface covering material.

To produce a surface covering having the desired pattern without the use of special equipment or excessive horsepower, the binder system of the present invention contains about 30% to about 70% by weight of poly vinyl chloride and about 70% to about 30% by weight of the diisocyanate-modified polyester. When less than about 30% by weight of the polyester is found in the binder composition, the composition is too tough and requires excessive horsepower and equipment of great strength in order to work the composition. When more than about 70% by weight of the polyester is present, the material is too elastic to be worked,and it is difficult to obtain the desired pattern in the finished floor covering. i

Generally speaking, the binder comprises about 50% to about 25% by weight of the wearing surface composition. The binder is admixed with filler, including pigment, in such proportions that filler comprises about 5 0% to about 75% by weight of the composition. When the filler content is below about 50%, pattern control may be difiicult. filler is present, the physical properties of the finished surface covering materials do'not measure up to the desired standards, particularly in'the floor covering art. Particularly advantageous results have been obtained when the filler includes a preponderant proportion by volume of fibrous filler, such as wood flour, cork particles, asbestos, mineral fibers, and the like. The remainder of the filler component is comprisedof finely divided particles, such as Whiting, clay, silica, slate flour, and similar nonfibrous filler material. Also included in the filler component are small but effective amounts of lubricants and detackifying agents, such as, for example, stearic acid,parafiin wax, ceresin wax, oleic acid, lauric acid, Many of the advantages of the present invention result from the fact that the diisocyanate-modified polyester used therein is sulfur-curable. Thus, vulcanizing agents and curing accelerators are also to be added to the filled composition. Thus, there may be added sulfur, or sulfur-containing compounds, along with When more than about 75 by weight of by a Mooney plasticity of about 20 points to points at 212 F. When plasticity of the composition is below 20' points, the finished surface covering material has too little strength. On the other hand, when the plasticity is more than about 80 points, the material is so tough that it is exceedingly diflicult to process. This plasticity 'of the composition may be obtained in a number of ways. For example, the degree of cross linking of the modified polyester may be controlled so that the polyester may be a comparatively soft and elastic gel, and hence when combined with polymerized vinyl halide, it imparts a high order of plasticizing action to-the final blend. Another method of obtaining the desired plasticity in the composition to be calendered. is that involving the addition of still another plasticizer or plasticizers to the blend of polyester and vinyl resin. Typical plasticizers which may be incorporated into the composition to be calendered are dioctyl phthalates, dicapryl phthalate, dibutyl sebacate, dibutoxy ethyl phthalate, tricresyl phosphate, and other known plasticizers. If desired, the plasticity may be obtained by a combination of these technics. Compositions containing as the binder component about 39% toabout 53% by weight of polyvinyl chloride and about 30% to about 44% by weight of the modified polyester and between about 10% and about 24% by weight of additional plasticizer are particularly suitable for calendering into a sheet to produce a surface covering material.

As can be seen from the above, the compositions comprise a binder containing polymerized vinyl halide, preferably polyvinyl chloride, and a diisocyanate-modified polyester. It is also possible to utilize a composition which contains other ingredients besides the basic binder components. For example, vinyl chloride-vinyl acetate copolymer may be incorporated into the binder, as well as synthetic rubber, such as butadiene-styrene copolymers, butadiene-acrylonitrile copolymers, chloroprene polymers, and the like. Additionally, a portion of the binder may be replaced by additional and different polyesters.

In producing the composition to be calendered, the ingredients are weighed and mixed in an intensive mixer, such as a Banbury. The resulting mixture is then subjected to further mixing on a mill, followed by cooling of the mix. The slab from the mill may then be subdivided to the desired particle sizes, and the resulting mixture of finely divided particles may be passed through a calender in an operation to be described more fully below.

In the preferred embodiment of the plastic surface covering preparation, the loose mass of particles, which is subjected to the operations of the calender, is such that :the preponderant proportion is in the range of about 8 assaesa pleted formulation may be calendered into a sheet, which may be applied to a backing at the same or a subsequent stage of the process. The backing material may be any of a number of materials employed in the production of resilient surface covering material. For example, it may be burlap or a saturated felt such as an asphalt-saturated felt, a resin-saturated felt, or a felt which has been coated with rubber or synthetic rubber, as by the beater saturation process. Thus, the fabric backing will include such materials as woven fabric, for example burlap, canvas, or cotton sheeting, and feltered products such as saturated felt.

The composition obtained as indicated above is calendered into a sheet by passing the material through a calender, in which the face roll is generally but not always at a lower temperature than the back roll. The temperature of the roll varies, depending upon the desired pattern. For example, to obtain plain or striated effects, the face roll temperature should be in the range of about 80-l50 F. Generally speaking, the temperature of the back roll is advantageously maintained at a temperature of about 80220 F.

Following the production of the sheet as indicated above, the material is then cured at elevated temperatures. The cure may be accomplished in curing presses, but particularly advantageous results have been obtained by suspending the material in air and heating the suspended material at elevated temperatures. In order to obtain maximum physical properties, it is advantageous to utilize comparatively high temperatures, such as 250 F. Good cures can be obtained in the range of about 210 F. to about 275 F. Higher temperatures than about 275 F. may result in an extraordinary degree of stove staining, which is disadvantageous, particularly in light-colored goods. Excellent results are obtained generally by curing the sheet in stoves at temperatures of about 250 F. for a period of time of about 8 to about 30 hours. The temperature should be raised gradually to prevent formation of blisters due to sudden exposure to heat. If desired, the final product may be given a high gloss by the application of lacquer and/ or wax after the curing operation.

Although such surface covering materials are particularly well suited for use as floor coverings, the materials may also be employed as a covering for walls, desk tops, counter tops, sink tops, table tops, and the like, in the form of sheet goods or tile.

The following examples illustrate several embodiments of the invention. All parts are by weight unless otherwise stated.

Example I To a three-liter, three-neck fiat fitted with sealed stirrer, an electrically heated reflux condenser attached to a water-cooled take-off condenser, an inlet for the admission of carbon dioxide, a thermal regulator, and a thermometer was added 643 parts (7.14 moles, 19% excess) 1,4-butanediol. The dried carbon dioxide flow rate was kept at 0.3 liter per minute, and the temperature of the 1,4-butanediol was increased to 80 C. To the heated 1,4-butanediol was added 304.3 parts (2 moles) tetrahydrophthalic anhydride. The anhydride was added slowly to the reaction mixture so there would not be a sharp decrease in temperature. Mixing was continued until a homogeneous solution was obtained, and then 584.8 parts (4 moles) adipic acid was added slowly to the hot stirred mixture. After all the adipic acid was added, the temperature was increased to 145 C. over a period of 30 minutes and held at that temperature for 1 hour. The-gas flow was kept at 0.3 liter per minute, and at a temperature of 145 C. some water started to distill off.

The temperature was then raised to 200 C. over a period of 90 minutes and maintained at that temperature until an acid number of 30i2 was obtained. The time required to reach that acid number was approximately 400 minutes. When an acid number of 30 was obtained,

the temperature of the mixture was raised to 230 C. over a period of 60 minutes and the flow of carbon dioxide was increased to 2.5 liters per minute. The temperature was maintained at 230 C. for 200 minutes, after which the temperature was increased to 245 C. over a 60-minute period and the gas fiow was increased to 3.5 liters per minute. The batch temperature was maintained at 245 C. until an acid number of 3-6 was obtained. The final hydroxyl number was 27. The polyester was then cooled.

Into a kettle equipped with an agitator was placed 2500 parts of the above polyester and the charge was heated to 260 F. (127 C.) with agitation. At that temperature, 110.2 parts, 2,4-toluene diisocyanate was added and the mixture was maintained at 260 F. with agitation for 30 minutes. This amount of diisocyanate was determined to be proper by withdrawing several samples of the bulk polyester and adding increasing amounts of the diisocyanate to each of the samples. After thorough mixing, the samples were gelled by being heated to 220 F. (104 C.) for 12 hours. The weight of the diisocyanate needed for "the 2500 parts of polyester was calculated from that sample which just reached the point of incipient gelation.

At the end of the 30-minute period of agitation of the 2500 parts of polyester, plus the diisocyanate, the mixture was a thick, viscous liquid which was poured from the kettle into a greased pan and allowed to cool. The gelling reaction was completed by placing the polyester in the greased pan in an oven heated at 220 F. for a period of 12 hours. At the end of that time, the modified polyester was a thick, viscous gum.

A blend utilizing the above-described modified polyester was then formulated into a resilient flooring composition in accordance with the following formula:

Parts Diisocyanate-modified polyester 265 Geon 126 (polyvinyl chloride resin) 265 Tricresyl phosphate 47 Whiting (ground limestone) 353 International fiber (mineral filler) 180 Wood flour 132 Stearic acid 4 Ceresin wax 8 Sodium monacid phosphate on clay filler 6 Mercaptobenzothiazole 8 Cupric dimethyldithiocarbamate 0.4 Sulfur 6 Alkyl phenoldisulfide 8 Zinc oxide 16 Titanium dioxide Example II To a five-liter, four-neck flask equipped as described in Example I was added 1928 parts (21.4 moles, 19% mole excess) 1,4-butanediol and 588 parts (6 moles) maleic anhydride. The mixture was heated, and after about 20 minutes, the maleic anhydride was in solution, and 1754 parts (12 moles) adiphic acid was added. The gas flow was maintained at 0.4 liter carbon dioxide per minute. After the adipic acid was added, the temperature of the mixture was increased to 140 C. over a period of 45 minutes and held at this temperature for minutes. Over a period of 225 minutes, the temperature of the polyester was increased to 200 C. and was maintained at 200 C. for 620 minutes. After an acid number of 15 was obtained, the temperature was increased to 215 C. over a period of 15 minutes and was held at that temperature for the remainder of the reaction cycle. The total reaction time for the preparation of this polyester was 1100 minutes, and the final acid number and hydroxyl number was 12 and 23, respectively.

500 parts of this polyester was converted to an incipient'gel by the addition of 2,4-toluene diisocyanate in accordance with Example .I; 18 parts of the diisocyanate was required.

terial. Example III A mixture of 1609 (17.88 moles, 19.2% mole excess) 1,4-butanediol and 820 parts moles) endomethylene tetrahydrophthalic anhydride was heated in a five-liter, four-neck flask equipped as described in Example I. After the endomethylene tetrahydrophthalic anhydride was dissolved, 1461 parts moles) adipic acid was added and the temperature was increased to 145 C. over a period of 50 minutes. The temperature was held at 145 C. for 120 minutes and was then increased to 200 C. over a period of 60 minutes. The gas fiow was maintained at 0.4 liter of carbon dioxide per minute. The temperature was held at 200 C. until an acid number of 10 was obtained. The whole time at 200 C. was approximately 615 minutes. Over a period of 60 minutes, the temperature was raised to 215 C. and the gas flow was increased at the same time to 4.0 liters per minute. The reaction was terminated when an acid number of 3.8 and a hydroxyl number of 40 was obtained. The total time required for the preparation of this polyester was 1630 minutes.

500 parts of the above-described polyester Was converted to an incipient gel at elevated temperature by the addition of 31.6 parts 2,4-toluene diisocyanate in the usual manner.

100 parts of the above-described diisocyanate-modified polyester was intimately blended on a mill with 150 parts of mill end scrap vinyl. Flooring materials fabricated from this binder had excellent properties.

I claim:

1. A binder system for surface covering materials comprising an intimately blended mixture of about 30%- 75% by weight diisocyanate-modified polyester and about 70%-25% by weight polymerized vinyl chloride, said modified polyester being the reaction product of 0.6- 0.9 equivalent of organic diisocyanate per equivalent of unmodified polyester sufficient to form an incipient gel, said unmodified polyester having an acid number in the range of about 2-15 and a hydroxyl number in the range of about 20-55 and being formed from a saturated glycol having 4 carbon atoms, a saturated dicarboxylic acid having 6-10 carbon atoms, and an unsaturated compound selected from the group consisting of a dicarboxylic acid possessing a single ethylenic bond and no more than 8 carbon atoms, and the anhydride thereof, said saturated acid and said unsaturated compound being present in a mole ratio of about 2: 1.

2. A binder system according to claim 1 wherein said polymerized vinyl chloride comprises polyvinyl chloride.

3. A binder system according to claim 1 wherein said glycol comprises 1,4-butanediol.

4. A binder system according to claim 1 wherein said organic diisocyanate comprises 2,4-toluene diisocyanate.

5. A binder system according to claim 1 wherein said acid number is in the range of about 4-6 and said hydroxyl number is in the range of about 30-40.

6. A binder system according to claim 1 comprising about 50% by weight of said diisocyanate-modified polyester and about 50% by weight of said polymerized vinyl chloride.

7. A binder system for surface covering materials comprising an intimately blended mixture of about 30%- 75% by weight diisocyanate-modified polyester and about 70%-25% by Weight polyvinyl chloride, said modified polyester being the reaction product of 0.6-0.9 equivalents 2,4-toluene diisocyanate per equivalent of unmodified polyester to form an incipient gel, said unmodified polyester having an acid number in the range of about 2-15 and a hydroxyl number in the range of about 20- 55 and being formed from 1,4-butanediol, adipic acid, and tetrahydrophthalic acid, said adipic acid and said tetrahydrophthalic acid being present in a mole ratio of about 2:1.

8. As a new article of manufacture, a cured surface covering material comprising a binder system and a filler, the filler being present in an amount in the range of about l5%-75% by weight, the binder system comprising an intimately blended mixture of about 30%- 75% by weight diisocyanate-modified polyester and about 70%-25% by Weight polymerized vinyl chloride, said modified polyester being the reaction product of 0.6-0.9 equivalent of organic diisocyanate per equivalent of unmodified polyester sufiicient to form an incipient gel, said unmodified polyester having an acid number in the range of about 2-15 and a hydroxyl number in the range of about 20-55 and being formed from a saturated glycol having 4 carbon atoms, a saturated dicarboxylic acid having 6-10 carbon atoms, and an unsaturated compound selected from the group consisting of a dicarboxylic acid possessing a single ethylenic bond and no more than 8 carbon atoms, and the anhydride thereof, said saturated acid and said unsaturated compound being present in a mole ratio of about 2:1.

9. A surface covering material according to claim 8 wherein said glycol comprises 1,4-butanediol, said saturated dicarboxylic acid comprises adipic acid, and said unsaturated compound comprises tetrahydrophthalic anhydride.

10. A surface covering material according to claim 8 wherein said polymerized vinyl chloride comprises polyvinyl chloride.

11. The method of forming a binder system for surface covering materials which comprises reacting a saturated glycol having 4 carbon atoms, a saturated dicarboxylic acid having 6-10 carbon atoms, and an unsaturated compound selected from the group consisting of a dicarboxylic acid possessing a single ethylenic bond and no more than 8 carbon atoms, and the anhydride thereof, said saturated acid and said unsaturated compound being present in a mole ratio of about 2:1, to form an unmodified polyester having an acid number in the range of about 2-15 and a hydroxyl number in the range of about 20-55, adding just sufiicient organic diisocyanate in the range of 0.6-0.9 equivalent of said organic diisocyanate per equivalent of said unmodified polyester to said unmodified polyester to form an incipient gel at a temperature in the range of about 100-l50 C., and intimately blending said gelled polyester with polymerized vinyl chloride to form a binder system containing about 30%-75% by Weight of said diisocyanate-modified polyester.

12. The method according to claim 11 wherein said organic diisocyanate comprises 2,4-toluene diisocyanate, said saturated dicarboxylic acid comprises adipic acid, said glycol comprises 1,4-butanediol, and said unsaturated compound comprises tetrahydrophthalic anhydride.

13. The method of forming a surface covering material which comprises blending %-25 by weight of the binder system prepared according to claim 11 with 15%-75% by weight filler and curing the resulting composition in air at elevated temperature in the range of about 2l0-275 F.

14. The method according to claim 13 wherein said blend includes a sulfur-containing curing system.

References Cited in the file of this patent UNITED STATES PATENTS 2,606,162 Coffey Aug. 5, 1952 2,625,531 Seeger Jan. 13, 1953 2,698,838 Simon et al. Jan. 4, 1955 2,777,831 Seeger et a1 Jan. 15, 1957 2,780,613 Rubens Feb. 5, 1957 

1. A BINDER SYSTEM FOR SURFACE CONVERING MATERIALS COMPRISING AN INTIMATELY BLENDED MIXTURE OF ABOUT 30%75% BY WEIGHT DIISOCYANATE-MODIFIEN POLYESTER AND ABOUT 70%-2K BY WEIGHT POLYMERIZED VINYL CHLORIDE, SAID MODIFIED POLYESTER BEING THE REACTION PRODUCT OF 0,60.9 EQUIVALENT OF ORGANIC DIISOCYANTE PER EQUIVALENT OF UNMODIFIED POLYESTER SUFFICIENT TO FORM AN INCIPIENT GEL, SAID UNMODIFIED POLYESTER HAVING AN ACID NUMBER IN THE THE RANGE OF ABOUT 2-15 AND A HYDROXYL NUMBER IN THE RANGE OF 20-55 AND BEING FORMED FROM A SATURATED GLYCOL HAVING 4 CARBON ATOMS, A SATURATED DICARBOXYLIC ACID HAVING 6-10 CARBON ATOMS, AND AN UNSATURATED COMPOUND SELECTED FROM THE GROUP CONSISTING OF A DICARBOXYLIC ACID POSSESSING A SINGLE ETHYDRIDE BOND AND NO MORE THAN 8 CARBON ATOMS, AND THE ANHYDRIDE THEREOF, SAID SATURATED ACID AND SAID UNSATUREED COMPOUND BEING PRESENT IN A MOLE RATIO OF ABOUT 2:1. 